Apparatus for three-dimensional integrated circuit device fabrication including wafer scale membrane

ABSTRACT

Apparatus configured for the fabrication of three-dimensional integrated devices and three-dimensional integrated devices fabricated therefrom are described. A device side of a donor wafer is coated with a polymer film and exposure of a substrate side to an oxidizing plasma creates a continuous SiO 2  film. Portions of the substrate side are selectively coated with a polymer film and etching of uncoated areas removes at least a substantial portion of the crystalline substrate. A plasma etch tool etches a crystalline substrate to within a pre-determined thickness. The silicon portions of the substrate side are etched by exposure to TMAH. After etching, the donor semiconductor wafer is supported by portions of the substrate that were not etched. The supporting structure allows flexing of the donor semiconductor wafer within the etched areas to enable conformality and reliable bonding to the device surfaces of an acceptor wafer to form a three dimensional integrated device.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional and claims priority from U.S. patentapplication Ser. No. 12/172,452 filed on Jul. 14, 2008, now ______, theentire disclosure of which is herein incorporated by reference.

FIELD OF THE INVENTION

The present invention relates generally to silicon circuit devices andfabrication techniques, and more particularly to fabricatingthree-dimensional integrated circuit devices.

BACKGROUND OF THE INVENTION

The stacking of integrated circuits and discrete devices in threedimensions enables advanced Chip Packaging, CMOS, and mixedCMOS/Photonics/RF technologies and applications. An inability toprecisely align structures and bond them to each other with minimumyield impact is a major limitation to three-dimensional integratedcircuit fabrication. Many process schemes are employed to transferdevices from one Si wafer and stack them on devices fabricated onanother Si wafer. Generally either direct bonding of two Si wafers withthe subsequent removal of one (donor) substrate, or a (donor) layertransfer to a disposable “handle” substrate with subsequent bonding andhandle substrate removal are methods used for circuit and device level3D integration. These processes have limitations that inducemanufacturing complexity and can reduce yields.

Directly bonding two silicon wafers face to face and selectivelygrinding and etching one to leave a transferred device layer is anoption that does not involve processing of thermally dissimilarmaterials. In the device or circuit alignment procedure, however, thistechnique does not allow direct viewing of alignment patterns andthrough wafer imaging using infrared light is often used to see througheach Si wafer during the alignment procedure. Transfer of device layersfrom donor substrates to transparent “handle” substrates allows directoptical alignment of patterns, but introduces pattern shifts and yieldlimitations as a result of unmatched thermal characteristics andsubstrate flatness variations.

Three-dimensional integrated circuit fabrication techniques also oftensuffer from process induced pattern specific voiding at the bondingsurface. Such voiding is often very difficult to control and reducesproduct yields.

Therefore a need exists to overcome the problems with the prior art asdiscussed above.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, a method forfabricating three-dimensional integrated circuits includes etching acrystalline substrate within an area of a substrate side of a donorsemiconductor wafer, the substrate side having a substrate thickness andbeing located opposite a device side of the donor semiconductor wafer,to remove at least a substantial portion of the crystalline substratewithin the area. The method further including supporting the donorsemiconductor wafer with a supporting structure. The supportingstructure allowing flexing of the donor semiconductor wafer within atleast a portion of the area after the etching.

In accordance with another aspect of the present invention, athree-dimensional integrated circuit fabrication apparatus includes anetching tool adapted to etch crystalline substrate within an area of asubstrate side of a donor semiconductor wafer. The substrate side has asubstrate thickness and is located opposite a device side of the donorsemiconductor wafer. The etching tool removes at least a substantialportion of the crystalline substrate within the area. Thethree-dimensional integrated circuit fabrication apparatus furtherincludes a supporting structure adapted to support the donorsemiconductor wafer. The supporting structure allowing flexing of thedonor semiconductor wafer within at least a portion of the area afterthe etching.

In accordance with another aspect of the present invention, athree-dimensional integrated semiconductor device includes at least aportion of an acceptor wafer comprising a first device layer and atleast a portion of a donor wafer with a second device layer bonded tothe first device layer. The donor wafer has a crystalline substrate thathas been substantially removed from the at least a portion of the donorwafer prior to being bonded to the first device layer, thereby allowingthe second device layer to flexibly conform to the first device layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying figures, where like reference numerals refer toidentical or functionally similar elements throughout the separate viewsand which together with the detailed description below are incorporatedin and form part of the specification, serve to further illustratevarious embodiments and to explain various principles and advantages allin accordance with the present invention.

FIG. 1 illustrates a Silicon on Insulator (SOI) semiconductor wafer pairadapted to be fabricated into a three-dimensional semiconductor circuit,in accordance with one embodiment of the present invention.

FIG. 2 illustrates a substrate etched second SOI semiconductor wafer, inaccordance with one embodiment of the present invention.

FIG. 3 illustrates an alternative substrate etched second SOIsemiconductor wafer, in accordance with one embodiment of the presentinvention.

FIG. 4 illustrates a partitioned wafer substrate side of a second SOIsemiconductor wafer, in accordance with one embodiment of the presentinvention.

FIG. 5 illustrates a two wafer bonding arrangement, in accordance withone embodiment of the present invention.

FIG. 6 illustrates a semiconductor device membrane with a separatesupport structure, in accordance with one embodiment of the presentinvention.

FIG. 7 illustrates a processing flow diagram for a second devicemembrane bonding process, in accordance with one embodiment of thepresent invention.

FIG. 8 illustrates a selective die bonding arrangement, in accordancewith one embodiment of the present invention.

DETAILED DESCRIPTION

While the specification concludes with claims defining the features ofthe invention that are regarded as novel, it is believed that theinvention will be better understood from a consideration of thefollowing description in conjunction with the drawing figures, in whichlike reference numerals are carried forward.

One embodiment of the present invention provides a device transferoption that does not use lamination to a “handle” substrate. An ultrathin (generally less than 1 μm), transparent film that containselectrical devices, such as electronic or opto-electronic circuits iscreated from a conventional wafer by removing most or all of the bulksubstrate. The ultra thin, transparent film facilitates the highestpossible bonding alignment accuracy between the two die or wafers byallowing optical sensing of a mating wafer surface through the film.Once bonded, this ultra-thin, transparent film easily conforms topattern specific topography of the surface to which it is bonded andallows diffusion of volatile species during a bond anneal cycle. All ofwhich represent yield improvements with respect to conventional devicelayer transfer options.

One embodiment of the present invention provides a layer transfertechnique that creates a thin (usually <10 μm thick and more commonlyabout 1 μm thick) membrane that is the size of an entire semiconductorwafer. The thin membrane contains semiconductor devices, such aselectronic or opto-electronic circuits. This thin membrane in oneembodiment is created using a combination of RIE etching and wet etchingprocesses to remove all or selected portions of the crystalline siliconsubstrate of a semiconductor wafer. This thin membrane is designed andintended to be bonded to another semiconductor die or wafer to createthree-dimensional integrated circuit devices.

The thin membrane that contains the desired semiconductor structures issupported by a supporting structure. One embodiment of the presentinvention uses a ring of full thickness crystalline silicon at the waferedge that is not etched from the bulk silicon substrate of the wafer.Such a ring of full thickness crystalline silicon in one embodiment isalso supplemented by an optional grid of full thickness crystallinesilicon that is not etched from the bulk silicon substrate. The supportsin such a grid exist between, for example, one or more active deviceareas on the wafer. Yet another embodiment of the present invention isable to create a membrane that has all of the bulk Silicon substrateremoved and that is supported by a support structure that includes aseparate attached structural support. One embodiment of the presentinvention uses, for example, a glass/Pyrex support ring that is attachedto the circumference of the membrane before the silicon substrate isetched from the wafer.

FIG. 1 illustrates a Silicon on Insulator (SOI) semiconductor wafer pair100 adapted to be fabricated into a three-dimensional semiconductorcircuit, in accordance with one embodiment of the present invention. TheSOI semiconductor wafer pair 100 includes a first SOI semiconductorwafer 110 that is an acceptor semiconductor wafer for athree-dimensional integrated semiconductor device. The SOI semiconductorwafer pair 100 also includes a second SOI semiconductor wafer 120 thatis a donor semiconductor wafer for a three-dimensional integratedsemiconductor device. The first SOI semiconductor wafer 110 has a firstbulk silicon layer 112, a first buried insulator layer 114, and a firstdevice layer 116. The second SOI semiconductor wafer 120 has a secondbulk silicon layer 122, a second buried insulator layer 124, and asecond device layer 126. The first SOI semiconductor wafer 110 and thesecond SOI semiconductor wafer 120, including their buried insulatorlayers and device layers, of one embodiment of the present arefabricated using conventional means.

Although the example illustrated in the Silicon on Insulator (SOI)semiconductor wafer pair 100 of FIG. 1 uses a Silicon on Insulator (SOI)wafer as the acceptor semiconductor wafer, the illustrated embodimentand further embodiments of the present invention are able to operate byusing acceptor semiconductor wafers that consist of any type ofsubstrate, such as a bulk silicon wafer, GaAs or other types ofsubstrates, and are not limited to using SOI substrates for either theacceptor semiconductor wafer or the donor semiconductor wafer. Acceptorsemiconductor wafers of one embodiment are characterized by having asurface that is suitable for bonding to the donor semiconductor waferand as being suitable for the bonding process used to bond the donorsemiconductor wafer to the acceptor semiconductor wafer.

The first device layer 116 and the second device layer 126 of oneembodiment of the present invention include semiconductor circuits thatare intended to be fabricated so that the top of the first device layer116 will be positioned so as to face the second device layer 126.

The first SOI semiconductor wafer 110 further has a first bonding film118 placed on the first device layer 116 and the second semiconductorwafer 120 has a second bonding film 128 placed on the second devicelayer 126. As described below, one embodiment of the present inventionforms a three-dimensional semiconductor circuit by locating the firstSOI semiconductor wafer 110 in proximity to the second SOI semiconductorwafer 120 and bonding the SOI semiconductor wafers together by placingthe first bonding film 118 in contact with the second bonding film 128so as to cause the first device layer 116 to be facing and preciselyaligned to the second device layer 118.

FIG. 2 illustrates a substrate etched second SOI semiconductor wafer200, in accordance with one embodiment of the present invention. Thesubstrate etched second SOI semiconductor wafer 200 of one embodimentcorresponds to the second SOI semiconductor wafer 120, described above,after it has been partially processed according to one embodiment of thepresent invention. The substrate etched second SOI semiconductor wafer200 of one embodiment is an entire semiconductor wafer, such as a 200 mmsilicon wafer or a 300 mm silicon wafer in some embodiments of thepresent invention.

The substrate etched second SOI semiconductor wafer 200 includes an areathat is an etched region 204 in which the bulk silicon substrate hasbeen completely etched to the second buried insulator layer 124 with theexception of a support ring 210. In one embodiment, the support ring 210is a about one centimeter wide and extends along the entire outer edgeof the semiconductor wafer. The etched second SOI semiconductor wafer200, which corresponds to the second SOI semiconductor wafer 120,includes, within the area, the second buried insulator layer 124 thesecond device layer 126, and the second bonding film 128.

The second SOI semiconductor wafer 120 of one embodiment is processed toform discrete transistors or circuits to be transferred to the first SOIsemiconductor wafer 110 and to be stacked on another layer ofdevices/circuits. The second SOI wafer 120 of one embodiment is preparedin the usual manner for bonding of its device layer to the device layerof the first SOI semiconductor wafer 110.

Once the first SOI semiconductor wafer 110 and the second SOIsemiconductor wafer 120 are prepared, the front side, i.e., the deviceside, of the second SOI semiconductor wafer 120 is coated with a polymerfilm 206 that is known to be resistant to caustic, high temperature etchchemistries such as tetramethylammonium hydroxide (TMAH) used in the artfor silicon etching. This polymer film in one embodiment is processedper vender specification to ensure optimum performance.

One embodiment of the present invention supports the thin membrane thatincludes the second device layer 126 and the second buried insulator 128with a ring 210 of crystalline silicon along the outer edge of thesecond SOI semiconductor wafer 120. In such embodiments, the backside(i.e., the side opposite the front side or the device side) of thesecond SOI semiconductor wafer 120 is then coated with polymer materialso as to cover an outer annular ring of substrate that is located closeto the edge and bevel surface of the second SOI semiconductor wafer 120.This outer annular ring defines a crystalline silicon structure that isto be a support ring 210. In one embodiment, the outer annular ringdefining the support ring 210 has a width of about one centimeter. Thepolymer film that is coated on a part of the backside of the second SOIsemiconductor wafer 120 is then annealed per vender specification. Oncethe polymer film is cured, the backside of the second SOI semiconductorwafer 120 is exposed to oxidizing plasma for several minutes to ensure acontinuous native SiO₂ film.

Once the substrate is coated in its portions that are not to be etched,the second SOI semiconductor wafer 120 is loaded in a plasma etch toolwhich is specifically designed to etch crystalline silicon at high ratesin a directional, or semi directional manor. In one embodiment, anAlcatel Deep Silicon RIE is used. A reactive gas chemistry containingSF₆ and O₂ is used in this embodiment to etch the silicon at a rateof >60 μm per hour. The etch chuck in this example is configured in sucha way that the clamping ring also protects a part of the polymer coatingthat covers the annular ring defining the support ring of the second SOIsemiconductor wafer 120. The dry etch of one embodiment is timed to stopwith about 100-200 μm of silicon wafer remaining within the etching area204. A further embodiment of the present invention includes aspecifically designed wafer clamp mechanism that provides protection ofthe entire support ring area of the substrate during the dry etchingprocess.

Once the second SOI semiconductor wafer 120 has been thinnedsubstantially, as described above, it is exposed to TMAH at aconcentration and temperature known to etch silicon at high rates whilebeing selective to SiO₂. Areas that have been protected with the polymerfilm are unaffected by this etching process. When the crystallinesilicon clears and the buried insulation layer 124 of the second SOIsemiconductor wafer 120 is exposed, in one embodiment, the second SOIsemiconductor wafer 120 is removed from the etch and rinsed with water.

A final preparation step includes removing the protective polymer filmeither by exposure to an O₂ plasma, or alternatively using aconventional organic stripper.

FIG. 3 illustrates an alternative substrate etched second SOIsemiconductor wafer 300, in accordance with one embodiment of thepresent invention. The alternative substrate etched second SOIsemiconductor wafer 300 is similar to the substrate etched second SOIsemiconductor wafer 200 described above, except that the second bulksilicon layer 122 is not completely etched so as to expose the secondburied insulator area 124 but rather leaves a silicon layer 302. Thesilicon substrate of the alternative substrate etched second SOIsemiconductor wafer 300 is etched to a depth that leaves a silicon layer302 that has a predetermined thickness. The predetermined thickness ofthe silicon layer 302 is able to be selected based upon the intendedapplication for the alternative substrate etched second SOIsemiconductor wafer 300.

FIG. 4 illustrates a partitioned wafer substrate side of a second SOIsemiconductor wafer 400, in accordance with one embodiment of thepresent invention. The partitioned wafer substrate side 400 of thesecond SOI semiconductor wafer 400 shows a silicon substrate supportring 404, that corresponds to support ring 210 described above. In oneembodiment of the present invention, the support ring 404 consists of aone centimeter (1 cm) ring of silicon substrate that is not etched bythe above described etching process.

In addition to the support ring 404, the partitioned wafer substrateside of a second SOI semiconductor wafer 400 includes additional supportpartitions that further divide the area of the wafer into a grid withsections consisting of one or more die on the wafer. In the illustratedexample, a first cross-support 414 and a second cross-support 416 extendparallel to one another across the wafer from one point of the supportring 404 to a point across the support ring 404. The first cross-support414 and the second cross-support 416 are aligned with and cover theedges of individual die on the wafer of the partitioned wafer substrateside of a second SOI semiconductor wafer 400.

The partitioned wafer substrate side of a second SOI semiconductor wafer400 further has a first dividing support 408 and a second dividingsupport 410 that are parallel to each other and extend perpendicularlybetween the first cross-support 414 and the second cross-support 416. Aselected die 412 is shown to be within the area that is bordered by thefirst cross-support 414, the second cross-support 416, the firstdividing support 408 and the second dividing support 410. As discussedbelow, one embodiment of the present invention allows for the selectiveengagement of the selected die 412 when forming three-dimensionalintegrated circuits.

One embodiment of the present invention creates the additional supportpartitions by lithographically patterned areas that overlay the chipkerf areas. These areas are protected, for example, by a combination ofdielectric film and a TMAH resistant polymer during the above describedsubstrate etching phase.

The additional support partitions of one embodiment create a structurethat provides support across the membrane and reduces potentialdistortions to the membrane. The additional support partitions furtherallow for individual chips or die to be bonded to portions, such asindividual die, of the first SOI semiconductor wafer 110 and selectivelyremoved so as to allow using only known good die on the second SOIsemiconductor wafer 110.

One embodiment of the present invention that incorporates additionalsupport partitions on the second SOI semiconductor wafer 120 include amodified membrane holder assembly that allows control the back sidepressure within each section that is defined by the additional supportpartitions. One embodiment of the present invention allows sections thatcorrespond to individual die on the second SOI semiconductor wafer 120to be defined by additional supports within the second SOI semiconductorwafer 120. Such embodiments allow, for example, selective bonding onedie on the second SOI semiconductor wafer 120 to a corresponding die onthe first SOI semiconductor wafer 110. The membrane holder of suchembodiments is able to have the ability for selective chip level releaseof the membrane once a bond has been initiated.

Another benefit of defining grids within the second SOI semiconductorwafer 120 by incorporating additional support partitions is that partsor all of the membrane can be transferred to an acceptor substrate,i.e., a wafer corresponding to the first SOI semiconductor wafer 110,that does not have the same form factor as the second SOI semiconductorwafer 120. Examples of such an application includes mixed technologyintegration when substrate form factors for the different functionalelements being combined are fabricated in different size or form factorsubstrates, such as GaAs lasers, CMOS devices, MEMS devices and thelike.

FIG. 8 illustrates a selective die bonding arrangement 800, inaccordance with one embodiment of the present invention. The selectivedie bonding arrangement 800 shows an acceptor semiconductor wafer 110with an acceptor device side 804 that is opposite a donor device side806 of a donor semiconductor wafer 802. As described below, theselective die bonding arrangement 800 allows one or more selected dieson the donor semiconductor wafer 802, such as known good dies known toexist on the donor semiconductor wafer 802, to be individually urgedinto contact with the acceptor semiconductor wafer 804.

The acceptor semiconductor wafer 110 of the selective die bondingarrangement 800 is shown to include a first bonding layer 118 and afirst device layer 116. The acceptor semiconductor wafer 110 is shown tohave an acceptor die 834 that is bordered by acceptor kerf areas 830.The various embodiments of the present invention support using acceptorsemiconductor wafer 110 that have various detailed structures and otherdetails of the acceptor semiconductor wafer 110 are not shown in thisillustration to simplify the description on the selective die bondingarrangement 800.

The donor semiconductor wafer 802 of the selective die bondingarrangement 800 is shown to have layers of the donor semiconductor wafer802 that correspond to the layers of the second SOI semiconductor wafer120, described above. The donor semiconductor wafer 802 includes aburied insulator layer 124, a device layer 126 and a bonding film 128. Adonor die 822 is shown to exist between donor kerf areas 832.

The donor semiconductor wafer 802 is attached to a supporting structurethat includes a support ring 812 and additional support partitions 810.In one embodiment, the additional support partitions 810 of theselective die bonding arrangement 800 are formed on kerf areas, such asthe donor kerf areas 832, of the donor semiconductor wafer 802 to form agrid structure defining a number of cavities, such as a first cavity820, a second cavity 822, a third cavity 824 and a fourth cavity 826.This grid structure is aligned with edges of die across the donorsemiconductor wafer and each cavity within the number of cavitiescircumscribes at least one die on the donor semiconductor structure.

One embodiment of the present invention operates to position the donorsemiconductor wafer 802 such that the donor device side 806 of the donorsemiconductor wafer 802 is in proximity to and removed from the acceptordevice side 804 of the acceptor semiconductor wafer 110. The positioningof the donor semiconductor wafer is able to be achieved by moving one orboth of the acceptor semiconductor wafer 110 and the donor semiconductorwafer 802. The positioning of one embodiment causes at least one die,such as the donor die 822, on the donor semiconductor wafer 802 to bealigned with a corresponding at least one acceptor die, such as theacceptor die 834 on the acceptor semiconductor wafer 110.

In one embodiment of the present invention, as illustrated by theselective die bonding arrangement 800, a selected donor die 822 isindividually urged into contact with the acceptor die 832. In oneembodiment, the donor die 822 is urged into contact with the acceptordie 832 by adjusting an internal pressure within the first cavity 820that is formed by the support structure formed by the support ring 812and additional support partitions 810. The selective die bondingarrangement 800 further allows selecting other dies that are on thedonor wafer to not be urged into contact with the donor semiconductorwafer. For example, an unselected die 840 that forms the bottom of thesecond cavity 824 has the internal pressure within its associatedcavity, i.e., the second cavity 824 in this case, adjusted so as tocause the unselected die 840 to not be urged into contact with theacceptor wafer 834. Such operations allow known bad dies to not beincluded in three-dimensional integrated circuits.

In one embodiment, the pressure within the number of cavities, such asthe first cavity 820, the second cavity 822, and so forth, is able to beindividually adjusted so as to allow for selective urging of portions ofthe donor semiconductor wafer 802. The individual portions of the donorsemiconductor waver 802 that can be selectively urged into contact witha corresponding portion of the acceptor semiconductor wafer in oneembodiment of the present invention is defined by the cavities formed bythe additional support partitions 810 and/or the support ring 812. Theportion that is able to be selectively engaged is able to include onedie, a pre-determined number of dies, and/or a field of the donorsemiconductor wafer 802 that is any size or configuration.

FIG. 5 illustrates a two wafer bonding arrangement 500, in accordancewith one embodiment of the present invention. The two wafer bondingarrangement 500 shows the first SOI semiconductor wafer 110 and thesecond SOI semiconductor wafer 120 positioned with their respectivedevice layers facing one another. The first device layer 116 of thefirst SOI semiconductor wafer 110 is facing the second device layer 126of the second SOI semiconductor wafer 120. Each of these device layersis further covered by a respective bonding film. The first device layer116 is covered by the first bonding film 118 and the second device layeris covered by the second bonding film 128.

The two wafer bonding arrangement 500 further includes a positioner 506that is able to adjust the relative position of the first SOIsemiconductor wafer 110 and the second SOI semiconductor wafer 120 so asto ensure their proper relative position prior to bonding these two SOIsemiconductor wafers into a three-dimensional semiconductor structure.Positioner 506 is controlled by a controller 504 that determines thecurrent relative positions of the two SOI semiconductor wafers anddetermines relative position adjustments to be made by positioner 506.

The etched region 204 of one embodiment of the present invention leavesan area of a substrate etched second SOI semiconductor wafer 200 thathas only three layers remaining, the second buried insulation layer 124,the second device layer 126 and the second bonding film 128. Someembodiments further leave a layer of crystalline Silicon that has apredetermined thickness 302. In some embodiments, these layers that formone surface of the etched region 204 are sufficiently thin so as toallow optical imaging through those layers. In such embodiments, asdescribed below, aligning the first SOI semiconductor wafer 110 and thesecond SOI semiconductor wafer 120 for bonding to one another isfacilitated by using optical imaging through those layers of thesubstrate etched second SOI semiconductor wafer.

The relative position of the first SOI semiconductor wafer 110 and thesecond SOI semiconductor wafer 120 in one embodiment is determined inpart by Controller 504 based upon feedback obtained through an opticalsensor 502. Optical sensor 502 captures an optical image of the firstdevice layer 116 that is visible through the first bonding film 118, thesecond bonding film 128, the second device layer 126 and the secondburied insulation layer 124. As discussed above, the second bonding film128, the second device layer 126 and the second buried insulation layer124 in one embodiment of the present invention form a sufficiently thinmembrane that allows an optical image of the first SOI semiconductorwafer 110 to be viewed and captured therethrough.

One embodiment of the present invention aligns and bonds the thinmembrane created from the second SOI semiconductor wafer 120 by 1)removing the protective polymer film 206 from the membrane's freesurface and completely preparing the underlying bonding oxide for fusionbonding to the first SOI semiconductor wafer 110; 2) cleaning both thesubstrates of the first SOI semiconductor wafer 110 and the second SOIsemiconductor wafer 120 and activating the first bonding oxide film 118and the second bonding oxide film 128 in a normal manner; and 3) loadingthe first SOI semiconductor wafer 110 and the second SOI semiconductorwafer 120 on to a modified bonding aligner.

A modified bonding aligner of one embodiment of the present inventionhas an ability to hold the donor substrate by applying vacuumexclusively to the outer silicon support ring 210 and an ability tocontrol the shape of a membrane by variation in internal pressure on thebackside membrane cavity, i.e., within the etched region 204. During thealignment process, the pressure on the back side of the membrane iscontrolled by adjusting a gas pressure so as to minimize bowing of themembrane. Once aligned, the membrane is controllably “bowed” towards thefirst SOI semiconductor wafer 110 by increasing the back gas pressurewithin the etched region 204 to a suitable level to conform the membraneto the topography of the top surface of the first SOI semiconductorwafer 110. The increased pressure further urges the membrane, of thedonor semiconductor wafer, into contact with the first device layer 116of the first SOI semiconductor wafer 110, thereby causing bonding of thedonor wafer to the acceptor wafer.

In the case of the waffle grid pattern, the application of pressure canbe controlled to ensure first a center region contact and bonding withgradual outward propagation of the applied pressure such that anyoutgased products are allowed to escape radially out.

Once the membrane, or a selected portion of the membrane, that is formedfrom the second SOI semiconductor wafer 120 is bonded to the surface ofthe first SOI semiconductor wafer 110, the combination of the supportedmembrane and the first SOI semiconductor wafer is annealed in acustomary fashion. In embodiments that bond the full wafer of the secondSOI semiconductor wafer 120 to the first wafer 110, the bondedcombination is annealed and the outer support ring, which is either theun-etched silicon substrate or a separate support structure, is removedvia a cutting or etching procedure.

FIG. 6 illustrates a semiconductor device membrane with a separatesupport structure 600, in accordance with one embodiment of the presentinvention. As discussed above, some embodiments of the present inventioncreates a membrane with a support structure that is formed by leavingcrystalline bulk silicon support ridges at selected locations across themembrane. As also discussed above, alternative examples of the supportstructure include a separate support ring around the edge of a donorwafer. Examples of the separate support ring include a glass/Pyrexsupport ring that is attached to the circumference of the membrane. Theseparate support structure is also able to include a waffle grid ofadditional support partitions for the donor wafer that operate similarlyto the above described additional support partitions. The additionalsupport partitions also act to control pattern distortions that mayoccur during the full wafer membrane formation process.

The semiconductor device membrane with a separate support structure 600illustrates an unattached separate support structure 610 that includes aseparate support structure 602. Embodiments of the present inventionthat utilize a semiconductor device membrane with a separate supportstructure 600 are able to include an alignment mark 606 to supportaccurate positioning of the separate support structure, and the attacheddonor wafer, during fabrication. The illustrated separate supportstructure 602 has a substrate pre-alignment notch 606 that supportspre-location of the donor wafer membrane pattern by a locking mechanismfor the separate support structure 602.

The semiconductor device membrane, such as a donor wafer, with aseparate support structure 600 illustrates an alternative to etching thecrystalline silicon substrate and leaving crystalline silicon ridges onthe membrane. The semiconductor device membrane with a separate supportstructure 600 illustrates a result of a process that attaches a separatesupport structure 602, such as a glass/Pyrex support ring, to the backside of the membrane 604 and then etches away the crystalline siliconsubstrate to remove the silicon substrate and, in on embodiment, exposethe buried oxide layer and thereby creates a donor wafer membrane. Anattached separate support ring first view 620 illustrates a donor wafermembrane 604 that is attached to a separate support structure. Theillustrated example of a separate support structure 602 includes only asupport ring attached to an outer portion of the circumference of thedonor wafer membrane 604 by anodic bonding. Similar bonding techniquesare used, for example, in the fabrication of x-ray mask substrates.Examples of separate support structures include rings that havethicknesses between, for example, 2 mm and 1 cm. In one embodiment ofthe present invention, the membrane 604 includes the second buriedinsulation layer 124, the second device layer 126 and the second bondingfilm 128. Further embodiments are able to use membranes that furtherhave a layer of crystalline Silicon substrate that has a predeterminedthickness 302.

An attached separate support ring side view 630 illustrates a cut-awayside view of the structure illustrated in the attached separate supportring first view 620. The separate support structure 602 has the donorwafer membrane 604 attached and is able to be mounted in a fabricationdevice to position the donor wafer membrane as required in proximity toan acceptor wafer to form a three-dimensional integrated circuit.

Embodiments of the present invention that utilize a semiconductor devicemembrane with a separate support structure 600 are able to providestructural support while having smaller edge exclusion regions. Suchembodiments further simplify masking of the backside of the second SOIsemiconductor wafer 120 during the dry and wet etch cycles and supportusing a method that confines the wet etch chemistry to the backside ofthe second SOI semiconductor wafer 120 so that polymer protective filmsare not needed. Embodiments that utilize the semiconductor devicemembrane with a separate support structure 600 are further able toprovide pre-alignment capability by aligning the second SOIsemiconductor wafer 120 to the separate support structure 602 andprovide a locator mechanism on an alignment tool that would ensure prealignment to 1 μm.

The separate support structure 602 of one embodiment is further able toinclude a waffle grid of additional support partitions that are similarto the additional support partitions described above. Such additionalsupport partitions of the separate support structure 602 are able to bedesigned to align with kerf areas of the membrane and provide supportalong the kerf areas of the membrane. Utilizing a separate supportstructure 602 with additional support partitions further allowsselective bonding of portions of the membrane, such as individual die,as is described above for the partitioned wafer substrate side of asecond SOI semiconductor wafer 400.

FIG. 7 illustrates a processing flow diagram for a second devicemembrane bonding process 700, in accordance with one embodiment of thepresent invention. The second device membrane bonding process 700performs the above described process of bonding a membrane that includesa second device layer 126 to a first SOI semiconductor wafer 110 inorder to create a three-dimensional semiconductor circuit.

The second device membrane bonding process 700 begins by creating, atstep 702, a first SOI semiconductor wafer with a first upper devicelayer and creating, at step 704, a second SOI semiconductor wafer with asecond upper device layer and a second silicon substrate, where thesecond silicon substrate is opposite the second upper device layer. Oneembodiment uses conventional processes to create the first SOIsemiconductor wafer and the second SOI semiconductor wafer.

The second device membrane bonding process 700 continues by placing, atstep 706, a first bonding film on the first upper device layer andplacing, at step 708, a second bonding film on the second upper devicelayer.

The second device membrane bonding process 700 continues by preparing,at step 710, the device, or front, side of the second SOI semiconductorwafer 120 for etching of the second silicon substrate. The preparationof the second SOI semiconductor wafer of one embodiment includes coatingthe device side of the second SOI semiconductor wafer 120 with a polymerfilm 206 that is known to be resistant to caustic, high temperature TMAHetch chemistries. This polymer film in one embodiment is processed pervender specification to ensure optimum performance.

Once the polymer film that was applied to the front, or device, side ofthe second wafer is cured, the backside (i.e., the side opposite thefront side or the device side) of the second SOI semiconductor wafer 120is exposed, at step 712, to oxidizing plasma for several minutes toensure a continuous native SiO₂ film.

The second device membrane bonding process 700 of one embodiment thatincorporates supporting structures for the device membrane by leavingportions of the second crystalline silicon substrate 122 next coat, atstep 714, the backside of the second SOI semiconductor wafer 120 withpolymer material that conforms to the supporting structure, such as byforming an outer annular ring 210 that is located close to the edge andbevel surface of the second SOI semiconductor wafer 120. The polymerfilm that is coated on the backside of the second SOI semiconductorwafer 120 is then annealed per vender specification.

Once the second crystalline silicon substrate is coated, the seconddevice membrane bonding process 700 etches, at step 716, the substrateto remove at least a portion of the crystalline silicon substrate 122.One embodiment of the present invention etches the second siliconsubstrate 122 by loading it into a plasma etch tool that is specificallydesigned to etch crystalline silicon at high rates in a directional, orsemi directional manor. In one embodiment, an Alcatel Deep Silicon RIEis used. A reactive gas chemistry containing SF₆ and O₂ is used in thisembodiment to etch the silicon at a rate of >60 μm per hour. The etchchuck in this example is configured in such a way that the clamping ringalso protects a part of the polymer coating defining the annular ringdefining the support ring of the second SOI semiconductor wafer 120. Thedry etch of one embodiment is timed to stop with about 100-200 μm ofsilicon wafer remaining within the etching area 204. A furtherembodiment of the present invention includes a specifically designedwafer clamp mechanism that provides protection of the entire supportring area during the dry etch.

Once the second SOI semiconductor wafer 120 has been thinnedsubstantially, as described above, the etching continues by exposing thesecond SOI semiconductor wafer 120 to TMAH at a concentration andtemperature known to practitioners of ordinary skill in the art to etchsilicon at high rates while being selective to SiO₂. Areas that havebeen protected with the thick polymer are unaffected by this etchingprocess. When the crystalline silicon clears and the buried insulationlayer 124 of the second SOI semiconductor wafer 120 is exposed, thesecond SOI semiconductor wafer 120 is removed from the etch and rinsedwith water.

The second device membrane bonding process 700 proceeds by removing, atstep 718, the protective polymer film either by exposure to an O₂plasma, or alternatively using a conventional organic stripper.

The second device membrane bonding process 700 continues by aligning andbonding, at step 720, the thin membrane created from the second SOIsemiconductor wafer 120 to the first SOI semiconductor wafer 110. Thealigning and bonding of one embodiment of the present inventionincludes 1) removing the protective polymer film 206 from the membrane'sfree surface and completely preparing the underlying bonding oxide forfusion bonding to the first SOI semiconductor wafer 110; 2) cleaningboth the substrates of the first SOI semiconductor wafer 110 and thesecond SOI semiconductor wafer 120 and activating the first bondingoxide film 118 and the second bonding oxide film 128 in a normal manner;and 3) loading the first SOI semiconductor wafer 110 and the second SOIsemiconductor wafer 120 on to a modified bonding aligner.

A modified bonding aligner of one embodiment of the present inventionhas an ability to hold the donor substrate by applying vacuumexclusively to the outer silicon support ring 210 and an ability tocontrol the shape of a membrane by variation in internal pressure on thebackside membrane cavity, i.e., within the etched region 204. During thealignment process, the pressure on the back side of the membrane iscontrolled by adjusting a gas pressure so as to minimize bowing of themembrane. Once aligned, the membrane is controllably “bowed” towards thefirst SOI semiconductor wafer 110 by increasing the back gas pressurewithin the etched region 204 to a suitable level to conform the membraneto the topography of the top surface of the first SOI semiconductorwafer 110.

It should be understood that these embodiments are only examples of themany advantageous uses of the innovative teachings herein. In general,statements made in the specification of the present application do notnecessarily limit any of the various claimed inventions. Moreover, somestatements may apply to some inventive features but not to others. Ingeneral, unless otherwise indicated, singular elements may be in theplural and vice versa with no loss of generality.

The circuit as described above is part of the design for an integratedcircuit chip. The chip design is created in a graphical computerprogramming language, and stored in a computer storage medium (such as adisk, tape, physical hard drive, or virtual hard drive such as in astorage access network). If the designer does not fabricate chips or thephotolithographic masks used to fabricate chips, the designer transmitsthe resulting design by physical means (e.g., by providing a copy of thestorage medium storing the design) or electronically (e.g., through theInternet) to such entities, directly or indirectly. The stored design isthen converted into the appropriate format (e.g., GDSII) for thefabrication of photolithographic masks, which typically include multiplecopies of the chip design in question that are to be formed on a wafer.The photolithographic masks are utilized to define areas of the wafer(and/or the layers thereon) to be etched or otherwise processed.

The method as described above is used in the fabrication of integratedcircuit chips.

The resulting integrated circuit chips can be distributed by thefabricator in raw wafer form (that is, as a single wafer that hasmultiple unpackaged chips), as a bare chip, or in a packaged form. Inthe latter case, the chip is mounted in a single chip package (such as aplastic carrier, with leads that are affixed to a motherboard or otherhigher level carrier) or in a multichip package (such as a ceramiccarrier that has either or both surface interconnections or buriedinterconnections). In any case, the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboard,or other input device, and a central processor.

Although specific embodiments of the invention have been disclosed,those having ordinary skill in the art will understand that changes canbe made to the specific embodiments without departing from the spiritand scope of the invention. The scope of the invention is not to berestricted, therefore, to the specific embodiments. Furthermore, it isintended that the appended claims cover any and all such applications,modifications, and embodiments within the scope of the presentinvention.

1. A three-dimensional integrated circuit fabrication apparatus,comprising: an etching tool adapted to etch crystalline substrate withinan area of a substrate side of a donor semiconductor wafer, thesubstrate side having a substrate thickness and being located opposite adevice side of the donor semiconductor wafer, to remove at least asubstantial portion of the crystalline substrate within the area; and asupporting structure adapted to support the donor semiconductor wafer,the supporting structure allowing flexing of the donor semiconductorwafer within at least a portion of the area after the etching.
 2. Thethree-dimensional integrated circuit fabrication apparatus of claim 1,wherein the area comprises an entire side of the substrate side, andwherein the supporting structure comprises one of a separate supportingstructure attached to the donor semiconductor wafer and portions of thesubstrate side that are outside of the area and that are not etched bythe etching.
 3. The three-dimensional integrated circuit fabricationapparatus of claim 1, further comprising: a wafer preparation tool thatis further adapted to: coat the device side of the donor semiconductorwafer with a first polymer film that is resistant to etchingchemistries; define the area by coating portions of the substrate sideoutside the area with donor polymer film that is resistant to etchingchemistries, wherein the etching tool is further adapted to: expose thesubstrate side to an oxidizing plasma to create a continuous nativesilicon dioxide film on a surface of the substrate side that is oppositethe device side; etch the substrate side with a plasma etch tool tosubstantially thin the crystalline substrate to within a pre-determinedthickness; and expose the substrate side to TMAH to etch siliconportions of the substrate side and not etch silicon dioxide portions ofthe substrate side; and wherein the supporting structure comprisesportions of the substrate side that are outside of the area and that arenot etched by the etching.
 4. The three-dimensional integrated circuitfabrication apparatus of claim 1, further comprising: a wafer bondingapparatus adapted to bond at least a portion of the device side of thedonor semiconductor wafer to a device side of an acceptor semiconductorwafer such that the flexing of the donor semiconductor wafer conformsthe device side of the donor semiconductor wafer to the device side ofthe acceptor semiconductor wafer.
 5. The three-dimensional integratedcircuit fabrication apparatus of claim 4, wherein the supportingstructure comprises a plurality of additional support partitions thatform a grid structure defining a plurality of cavities, the gridstructure being aligned with edges of die across the donor semiconductorwafer and each cavity within the plurality of cavities circumscribing atleast one die on the donor semiconductor structure, thethree-dimensional integrated circuit fabrication apparatus furthercomprising: a wafer positioner adapted to position, after the etchingand the supporting, the device side of the donor semiconductor wafer inproximity to and removed from the device side of the acceptorsemiconductor wafer, the positioning causing the at least one die on thedonor semiconductor wafer to be aligned with a corresponding at leastone die on the acceptor wafer, and wherein the wafer bonding apparatusis further adapted to adjust an internal pressure within one cavity ofthe plurality of cavities to urge at least one die circumscribed by theone cavity into contact with the device side of the acceptorsemiconductor wafer.
 6. The three-dimensional integrated circuitfabrication apparatus of claim 4, wherein the etching tool is furtheradapted to etch the crystalline substrate so as to allow light to passthrough a remainder of the donor semiconductor wafer, three-dimensionalintegrated circuit fabrication apparatus further comprising: a waferpositioner adapted to position the device side of the donorsemiconductor wafer in proximity to and removed from the device side ofthe acceptor semiconductor wafer, the positioning causing at least onedie on the donor semiconductor wafer to be aligned with a correspondingat least one die on the acceptor wafer, wherein the wafer positionerfurther comprises an optical sensor adapted to sense a position of theacceptor semiconductor wafer relative to the donor semiconductor wafer,and wherein the wafer bonding apparatus is further adapted to adjust aninternal pressure on a backside of the donor semiconductor wafer to urgethe device side of the donor semiconductor wafer into contact with thedevice side of the acceptor semiconductor wafer, wherein the backside isopposite the device side of the donor wafer.
 7. A donor wafer containingat least one integrated semiconductor device, the donor wafercomprising: a donor wafer membrane comprising a device layer and aburied insulating layer, the donor wafer being formed by substantiallyremoving a crystalline substrate from an area of a donor wafer, therebyallowing the device layer and the buried insulating layer within thearea to flexibly conform to an acceptor surface for bonding; and asupport structure attached to regions of the donor wafer membrane thatare outside of the area of the donor wafer membrane.